Particle accelerators produce high-speed, high-energy beams of particles that are utilized in a variety of applications, including radiation therapy, defense technology, imaging, and materials testing. A form of such particle accelerators, electron linear accelerators, are utilized for the sterilization of medical devices and food irradiation.
Traditionally, traveling wave accelerators have been used to achieve the goals of particle acceleration. Unfortunately, traveling wave accelerators have several disadvantages. First, the efficiency of a traveling wave accelerator is low, as the resulting particle beam contains particles that are not tightly bunched together. Second, the operating parameters of the traveling wave accelerators are fixed and there is little range for adjustment. Third, traditional traveling wave accelerators are not capable of producing particle beams at high intensities.
Some inventors have attempted to address these shortcomings by developing standing-wave linear accelerators. Generally, such standing-wave linear accelerators comprise an accelerating resonator, a radio-frequency generator that creates an accelerating field in the accelerating resonator, a solenoid that focuses the beam of particles, a vacuum pump, a power supply, and a control apparatus. The accelerating resonator commonly includes a biperiodic structure of accelerating cavities coupled to coupling cavities that operates in a π/2-mode. However, this structure alone is inefficient for capturing a large number of particles to bunch and form into a beam. Thus, some inventors have attempted to bunch the particles prior to accelerating the particles.
For example, some inventors have attempted to use designs incorporating a klystron-type buncher. In such a design, the klystron-type buncher and the accelerating resonator are coupled together via a drift space. Particles are bunched together in the klystron-type buncher and then drift through the drift space into the accelerating section for acceleration. Unfortunately, the presence of the drift space creates several disadvantages. First, as particles drift through the drift space, they begin to disperse and do not remain tightly bunched together. Thus, the amount of energy each particle receives in the accelerating section differs significantly which, in turn, creates a large amount of energy dispersion (10%–20%) in the resulting beam of accelerated particles. As a consequence, the overall efficiency of the linear accelerator is decreased. Second, a larger degree of energy dispersion occurs much more at higher intensities than at lower intensities. At very high intensities, the degree of the dispersion is so large that the linear electron accelerator cannot produce any bunches of particles in the resulting beam, which renders the linear accelerator useless at very high intensities. Thus, the large degree of dispersion at high intensities limits the possible applications for the linear accelerator.
Moreover, in systems having a bunching resonator and an accelerating resonator separated by drift space, two radio-frequency generators are typically required. One radio-frequency (RF) generator is required to create an accelerating field in the bunching resonator, and the other radio-frequency generator is required to create an accelerating field in the accelerating resonator. Because each resonator requires its own radio-frequency generator in such a design, the two radio-frequency generators must be in phase with one another for optimal particle bunching and acceleration. Changes in temperature or poor connections, among other factors, can cause the radio-frequency generators to become out of phase, which in turn causes instability in the accelerator system.
Therefore, there exists in the industry a need for standing-wave linear accelerators, including apparatuses and/or methods, which are capable of producing a tightly bunched beam of accelerated particles at high intensities with minimal energy dispersion, which receive electromagnetic power from a single RF generator, and which address these and other related, and unrelated, problems.